This invention relates to a method and apparatus for measuring retinal blood velocity in retinal capillaries utilizing the so-called "blue field entoptic phenomenon". "Entoptic" (i.e., within one's own eye) phenomena are visual perceptions of normal and abnormal structures in one's own eye.
Determining retinal blood flow is fundamental to an understanding of certain basic physiologic processes and pathologic conditions in the eye, and to evaluating objectively the treatment of certain ocular diseases. Quantitative measurement of retinal blood velocity and flow in the capillaries can be of particular importance. It is believed that the velocity of leukocytes in retinal capillaries is proportional to the flow of whole blood in these vessels. (Riva, Sinclair and Grunwald, Invest. Ophthalmol. & Vis. Sci. 21:34-38, 1981). At present, however, very little is known about the hemodynamics in retinal capillaries because of the lack of adequate measurement techniques.
The blue field entoptic phenomenon is the perception of one's own leukocytes (white blood cells) flowing in the macular capillaries of the retina. Vierordt, in 1860 (K. Vierordt, Grundriss der Physiologie (Meidinger, Frankfurt, 1860), suggested that the speed of blood flowing in retinal capillaries could be determined by measuring the speed of the leukocytes that one sees by means of the blue field entoptic phenomenon. Pursuing this idea, Kato (K. Kato, "The velocity of the blood stream in the retinal capillaries of the human eye. (The variation of the velocity of the blood stream after standing)", Acta. Soc. Ophthalmol. Jpn. 55, 1070-1078 (1971) Japanese) calculated the speed of the leukocytes by estimating the time it took the corpuscles to travel the length of a single capillary. In the method described by Hoffman and Podesta (D. H. Hoffmann and H. H. Podesta, "Zur Messung der Stromungsgeschwindigkeit in kleinsten Netzhautgefassen", Acta, XX Concilium Ophthalmologicum Germania, 1966. Edited by Weigelin E. Excerpta Medica, 1, 162-164 (1966)), subjects were asked to count the number of leukocytes that passed through one capillary in 30 seconds. Blood flow was determined from that number of leukocytes and their concentration in the blood.
The passage of leukocytes through a single macular capillary is difficult to observe for a prolonged time (M. Sint, E. Riehm and H. H. Podesta, "Untersuchungen uber die Beziehungen der zentralen kapillaren Retinadurchblutung zur Augendruckhohe bei Glaucompatienten mit Hilfe der entoptisch sichtbaren Blutbewegung", Klin. Mbl. Augenheilk., 171, 743-753 (1977). As a result, therefore, neither of the above-mentioned methods has become a routine clinical tool in retinal circulation examinations.
This invention relates to a novel method and apparatus for measuring the speed of leukocytes in retinal capillaries, the use of which eliminates the need for accurate tracking of a single capillary. The present method and apparatus calls on subjects to compare and match the appearance of the "global" motion of computer-simulated leukocytes with the appearance of the global motion of their own leukocytes, observed entoptically.
It is an object, therefore, of this invention to provide a novel method and apparatus for measuring quantitatively retinal blood velocity and flow, using the blue field entoptic phenomenon.
It is another object to provide a method and apparatus for measuring quantitatively retinal blood velocity and flow and which obviates the need for observing any single macular capillary for a prolonged time.
It is yet another object of this invention to provide a noninvasive and relatively quick method for measuring quantitatively retinal blood velocity and flow.
Other objects will appear hereinafter.